The placenta is a particularly attractive source of stem cells. Because mammalian placentas are plentiful and are normally discarded as medical waste, they represent a unique source of medically-useful stem cells. Provided herein are such isolated placental stem cells, populations of the placental stem cells, and methods of using the same to promote angiogenesis, and to treat disease or disorders of the circulatory system, e.g., diseases or disorders treatable by promoting angiogenesis.